CHEMICAL MANURES. 35 



Happily it is not so. The ideas which chemistry cannot furnish on 

 this head we can acquire by other means, and I add, that these pro- 

 cesses are not only the door of the agriculturist, but even enter into 

 his daily work. 



I have told you that plants are divided into two categories by the 

 relation to the different forms under which they assimilate azote. 

 Some take it from the air in the form of elementary azote, while 

 others draw it by preference from the soil in the form of ammonia 

 and nitrates. 



You know the consequence of this distinction. The plants which 

 draw azote from the air flourish in a soil deprived of it if they find 

 the three minerals of the complete fertilizer viz., phosphate of lime, 

 potash and lime. Plants which borrow azote from the soil, on the 

 contrary, become diseased and give but a poor produce. 



It follows from this that by the aid of these two little trials of 

 culture one can always know if the earth contains azotic matter and 

 the minerals. 



Cultivate peas and wheat, or peas and beets, alongside each other. 

 If the peas yield much and the wheat very little, you may without 

 hesitation conclude from that that the land, though provided with 

 minerals, is wanting in azotic matter. 



At Vincennes, when the earth had not received a fertilizer nothing 

 succeeded, which proved that it was destitute both of azote and the 

 minerals. 



These indications, although useful, are not sufficient for the ex- 

 igencies of practice. It needs more precise facts in regard to the 

 presence or absence of each component of the complete fertilizer ; 

 that is to say, the phosphate of lime, the potash, lime and azotic 

 matter. 



These new indications are as easy to obtain as the first, in the 

 following manner : 



Suppose you institute seven cultures of the same plant it may be 

 of the beet or wheat ; as you will. 



To the first give the complete fertilizer ; to the second, the same 

 fertilizer excluding azotic matter ; to the third, the complete fertilizer 

 deprived of phosphate of lime ; to the fourth, the complete fertilizer 

 less the potash ; to the fifth, less the lime ; to the sixth, less all the 

 minerals that is to say, reduced to the azotic matter ; the seventh 

 not having received any manure. 



It is very evident that if in the complete fertilizer the effect proper 

 to each component is manifest but as it is associated with three 

 others, the comparison of the returns obtained from the seven strips 

 of the little field ought to indicate what the soil contains and in what 

 it is wanting. 



In this system of investigation the culture with the complete 

 fertilizer becomes, in a measure, the invariable standard of compar- 

 ison to which are referred the returns of the other strips of ground, 

 and according as they approach or recede we conclude that the earth 

 contains or does not contain the element which has been voluntarily 

 excluded from the fertilizer. 



